I have found the answer. PostgreSQL creates index on primary key implicitly and can be seen via \d tablename; command on psql prompt. But PG_Admin-III does not show this index. Sorry to say that I faced several problems because of PG_Admin-III. And I advise you to use psql prompt instead of GUI.
From: Abdul Rahman <abr_ora@yahoo.com> To: pgsql-general@postgresql.org Sent: Wednesday, February 11, 2009 12:09:25 PM Subject: Key Vs Index
In Oracle, the index is automatically created during the creation of Primary Key. But in PostgreSQL either index is implicitly created of the user hast create it explicitly. I don't find any index against Primary Key and have to create index on this key.